Large bore hole drilling apparatus



J. G. JACKSON ETAL 3,195,661

LARGE BORE HOLE DRILLING APPARATUS 5 Sheets-Sheet 1 m2 mm Job fora 0n 066500,

Ve rrre Sin/fl INVENTQRS.

WHANN & McMAN/GAL Af/orneys for final/E0018, b I

AAA J w/ 4 July 20, 1965 Filed Oct. 15, 1959 y 20, 1965 J. G. JACKSON ETAL 3,195,661

LARGE BORE HOLE DRILLING APPARATUS 3 Sheets-Sheet 2 Filed Oct. 15, 1959 a n, 7 0 S s R 6 c M a M J EMJ a wu m MW Ham 8 m 0m Wm f M W 9 5 6 y 0, 1965 J. G. JACKSON ETAL 3,195,661

LARGE BORE HOLE DRILLING APPARATUS 3 Sheets-Sheet 3 Filed Oct. 15, 1959 S 4 2 m2 4 www c: 4 w A 4 j 4 4 4/ 4 a a e a w, 4 v 4 W 4 4 a v 4 2 4 4 w a z a w -I17, 4 4 m2 3M. 4 a 4 a a 4 4 5 9 5 .h/ 59 w 5 2 6 /l a w M 4 I r z 4 56 1M. 3 4 Q w. M n m a inventiofrif'relates to thelartof drilling here holes into the earth and 'relates more particularly' to apparatus fordrillings uch boreholes. i a

There is an increasing demand for large bore holes to inrov id'e' large diameter wells or large diameter pits" which may be used for underground storage; such as 'forisila'ge, or pits that may be used'ascyclone cellars. The diameter United,oS atesPatent "ice,

o'fsuch bore holeslmay he asgreat as "fe'et or even greaterl s The drilling or boring of such large diameterbore ho'les into the earth presents numerous problems and diflicblties; For eiiamplefremdval' of cuttings fromsaid' Bore holes as drillingoperations proceed'prese'rits' an extre'rrielydifli Qultprohlern." 1

It is therefore an object of the presenfinvention to pro vide'appa'ratus for driiling large bore holes into'thee'arth "whichwill' solve the problems encountered; i Itis another objectoftheinvention'to provide a a: ratus-of this characterhaving"a plurality'ofindepeni ently rotatable drilling-hits'havingannular paths which overlap each other to'cut'the desired large'di'arnter' bore a a. v t v- I" It isstill-another ohject of the invention to provide apparatus ofthis characterwherein'the drilling oitsha've a millingactionand can be moved in circular paths while cutting downward; H

A still further objectof the invention 'is'to provide apparatus of this character for effecting uniform action 'ofthe-varionsbits; H --Anotheror ject of the invention is to providemeans whereby there is eXtremely-"highhfting efiiciencyffor car rying away the cuttings in the drilling'of'large boreholes and the like. 1 Still another object of-thezinvenfion is to'pr'ovi'de means for carrying the cuttings awaywithout theirescaping past the bits into the-outerarmnhis; a A further objectof the invention'is'to provide apparatus for'pressurizing the bore hole. A still'further'object of the"invention' is'to provide means Whereby'the bits may be raised for"replacement Fepainor the-like; Another object of the invention is to 'provideapparatus of this character adapted to'prevent clogging 'or sticking or the drillingbits. Stillanother object of-the invention is to provide apparatusof this character for "glldll'lggth rotatingparts of the equipment, including-the drilling hits; his-a further object of the inventionto provide appa ratu s of thischaracter by means of whi'ch'iarge diameter holes may -be rapidlyand economicallyhoredintothe earthwn .-c 2 zA still-further object of theinv'ention is to provide'appa ratus of this character that may bereadily-transporfed-to a.;drilling. site:and* capable ofready assembly atsaid The characteristics and advantages of'theinventionare furtherisufiiciently referred to in connectionwith the following detailedwdescription, of the accompanying drawings which represent one arrangement. After, considering this example, skilled persons willunderstand.that-variations may be made withont departing. from the principles dis: dd d; a we qn empla the emp wmen o n step structures, arrangements; onmodes of operation that are properly within the scope of the appended claims.

-"Partaerated July-20,1965

" Referring tothe'drawingst' 1 FIG. 1 is a side elevational view"partlyjiri' 'seetion' of apparatiis' embedyingthe'jiresent invention;

"F1652 is an"'eniarged"se'ctional view of the drillin'g'iiiiit taken on line 2 2 of FIG} "1, ibro'vidirig a' plane View; of

" FIGI 4'is'a sectienal view taken en'li'ne tfe I'FIG. 2; FIG! S'is an enlarged longitudinal section" throngli one ofthedrilling bits'of the drallingunit;and PIG. 6 is a diagrammatic view of the p'cswer 'and'con eel system" or the; motor of {one'o'f we drillingbits or thedrilliiig'uriit/ Y Referringfrnore" particuiarlyito FIGfl, there is diagrammatically shown 'a" 'platf 'nn' 1t) "c mprising the flboryonwhich ader'r'ickll is mounted," said derrick b'eingofariy' 'vvel1'knownsliitable typ'el'." rhe'czher equipg merit required in j the drilling of wells is moi'mted in the platform of rig" fioor- 101'" equipments idfWell 'lrn5wn' ;character and includes a drawworks '15; with its engines is; There 'isals'oa jfotary' tabl'e eor t at well knbi n characte A g g At the earners of arepiazrorm' p' are pnen'm c aekg ing units 17 of Well known chara cte i, said ia cking ilfiits having vertical openings theretliroiigh for; 'slidah'le receptien of 'shpp0rt :o11injns l8 which a e of'is'te el and are pr "well mowa c a aaergs ia (261m ext'hding in the nsii'al' rnann'er into the formationto he thereby siipbort'e'd Belowthe latform Itlarid iri airial a 1ignriientwit'hjthe openin 'threugh the rbtarytaljl 16; there jis'la' Conductor? pipe 20 of larger diameter than thef'dia nieter'oithe'hore holato'fb'e dance." Conductor pi e 20' maybe r any suita le materialfhiit is "S awn" as b ing of reinforced concrete; said pipe fbeing'l'cylind r'icall in shape and being provided'at the bottom w h"aeannu arreenn 1 21 of surficient width to property support said conductor pipe, the footinghein'g'dishosedbeiieath the 'su'rjrace'ef thefor rna non, "as'hest Shawn 'iii'EIGL '1; it is to understood; of "coiirse, that theffooting" may; be disease ny suitahle manaerre providefpfo'pei siipp'ort fo'rth'e'co rictoriiifie. The upg'ir'portion of "the conductor pibe i's "preview witli a pair of annular :ieEess'eS 2 1 Which "extend about said greased w en Marmara a; 'crosls' sect'ionf'f'Anysuit: algle number or stich grbeve's; may remanded, the phrpose'ofsaid 'gr oove'sibeing desc'r'iheiiihereiinhftrl 'Aiiilot hole 251 s then drillfi into :the rdrm' 'tibntfi th'e desireid deptm whi hwoma basements; deeper t an thegdep'lthlto which manage diameter bore hole is to be drilled'j Byw'a'yef 'e'xar ri'rile, the pilot hole 25: may be 2 /2 feet in diameter and lis'fdrilledwiththe usual well nagreereeeng used. a

'-'1fhe 'l'ar'gediametr bore Zh oH ZG is d rille d with zi multiple 'bit drilling liifit; ifididltd ge nrally at V largediameter hole maybe twentytZO) teeter rnore i'n Unit ZS'mayliave -'a'r1y suitablejnui'nberfof hits hu't arrangement 'showmhas 'threel' There is, thereforeQa three-armed base p late 38 a1thoughthe platefit) maybe aorazeaaa bearing is'operablymounted'a hollow'shaft' 34 adaptedth Z rotate within said bearing. Collars and 36 are disposed on and secured to the shaft 34 at the lower and upper ends of the respective bearing 33 and said shaft is provided with external threads at the lower end for threadable reception in the internally threaded boxl38 of a bit, indicated generally at 40.

The body 41 of the bit has the usual arms 42 at the lower end thereof operably carrying the rotatable cutters 44. The lower end of the body 41 is provided with an axial'opening 45 therein in which is secured, by welding, or the like, an axially arranged tubular member 46, which extends upwardly and has its upper end terminating adjacent the upper end of the bit body, the upper end of said member 46 being d-isposed'within the box 38. As the outside diameter of the member 46 is substantially less than the diameter of the box 38, there is defined between said member and the'interior of the box 38 an annular passage or annulus, which extends downwardly from the lower end of said box, as indicated at 47. From the lower'end of the annulus 47 there is a passage 48 which extends downwardly through each of the respective arms 42, or the body. Within each of the passages 48 there is secured by press fitting, welding, brazing, or the like, an insert 49 having a passage 50 therethrough which is counterbored at the lower end, as indicated at 51; The counterbore 51 opens downwardly and a nozzle 52 is screwed thereinto, said nozzle having a passage 54 communicating at its upper end with the passage 50 of the insert 49 and discharging downwardly toward the respective cutting member 44.

The lower end of pipe 31 extends downwardly below the bits 40fand into the pilot hole 25, and at the lower end of said pipe 31 there is secured by the usual pin and box arrangement a reamer 58. A bit 59 of any well known construction is attached, by any well known means such as the well known pin and box arrangement, to the lower end of the reamer 58.

Spaced upwardly of the plate 30 there are three branch pipes having their inner ends connected to the pipe 31. The outer end of each pipe 65.has downturned portion 66 which extends into a swivel joint 68 secured to the upper end of the shaft 34. The swivel connection '68 providesmeans whereby the shaft 34 may rotate and there is packing means in said swivel connection to provide a fluid-tight connection between said swivel and the downturned end portion 66 of the branch pipe 65. Connections of this character are well known and it is believed to be unnecessary to show or describe same in detail.

Power means is provided for operating or rotating the bits 40. As shown there is secured an electric motor 76 on each arm of the plate 30. At one end of the shaft 71 of the motor there is secured a bevel gear 72 which meshes with a large bevel gear '73 secured to an adjacent portion of the shaft 34, it being understood, of course, that other means may be provided between the motor and the shaft 71 for eifecting rotation thereof.

. It is also to be understood that other power means may be employed to operate the bits 40. For example, by

draulic or air motor means may be used or mechanical power may be'provided and' transmitted from the surface to the bits. I V V V The upper end of the pipe 31 is secured to the lower end ofa drill string 75 by any usual well known means such as the pin and box arrangement commonly employed. I

Within the pipe '31 and drill string 75 there is another pipe, indicated at 76, which is of smaller external diameter than the internal diameter of the pipe 31 and said pipe 76 is connected to the lower end of a string of pipes of corresponding size which extends upwardly within the drill string 75 to provide a double, concentric drill string.

' 'The purpose of this arrangement is to provide a flow passage 78 between the inner and outer strings of pipe for the flow of drilling fluid, and a second flow passage 79 within the pipe 76 for flow of fluid in the opposite direction. In the arrangement herein disclosed, drilling fluid speed of the motor 70 is correspondingly respective tachometer 102.

flows downwardly in the annular ly in the passage 79.

In the Grable Patent No. 2,701,122, for Method and Apparatus Employing'Compressed Gas for Drilling Wells, there is disclosed apparatus for providing similar circulation of drilling fluid. The arrangement includes a swivel 86 which is connected to the drill string and interior string as shown in' said Grable patent, and the mechanism also includes a kelly 81 arranged similarly to the kelly of the apparatus of said Grable patent.

The lower end of the pipe 76 is provided with three branches 82 which extend within the branch pipes 65. Each of the pipes 82 have a swivel connection with the upper end portion 34 of a respective bit member 45a. The connection includes packing and is of known charactor. a

At the lower end of the pipe 76 there is a wall 85 having an axial opening therein for reception of the lower end of a conduit 86 of substantially smaller outside diameter than the inside diameter of the pipe 76, said conduit extending upwardly to the upper end of the pipe strings. Spaced downwardly of the wall 85 is a partition 87 in the pipe 31 which also has an axial opens ing therethrough. The lower end of conduit 86 is provided with a collar 88 which rests on the upper side of the wall 35 and below said wall there is a stationary packing gland 89.

The lower end of said gland 89 is connected by a short pipe 90 with a second stationarypacking gland indicated at 91, from the lower end of which there extends a short conduit 92 open at the bottom for reception of electric cables 94, each of which is provided with the wires which extend from a source of electric current to a motor 70. The cables 94 also include the wires for direct current electric tachometers, which are known in the art. The cables 94 extend upwardly through the conduit 86 and the respective wires of such cables are connected to annular rings 98, which are mounted on but insulated from a pipe portion'99 just below the swivel 80. This is a convenient'location for mounting these rings. The rings 98 are connected with respective wires 100 by means of respective brushes'ltll. This arrangement is diagrammatically shown, as devices for providing electrical con nections between rotating and stationary parts are well known.

Certain of the wires 100 are connected with tachometers 102 which may be suitably mounted in a support 103 on the platform It). The other wires ltltl-are connected to respective generators 105, FIG. 6, driven by any suitpassage 78 and upwardable variable speed means, such as a gas engine 106 or.

a diesel engine, or the like. The engine 106 is provided with a carburetor 107 which is connected by an actuatmg member 108 with a control lever, or the'like, 109, so that. actuation of the lever 109 functions tovary the opening of the carburetor throttle valve and hence vary the speed of the engine 166. i

The motors '70 are direct current motors and the generators are direct current generators. Each motor 76 is provided with itsown generator and each generator is provided with its own engine 106. By speed of the engine and hence of thegenerator105, the varied, and hence each motor 70 is provided with its own generator and eng1ne,.each'motor'is independently operable and its speed is variable independently of the speed of the other motors. The speed of each motor 70 is indicated by its variable speed type, and while a single motor is shown for each bit it is to be understood thatthere may be additional motors for the respective bits, or the motors may varying the be otherwise arranged. The important factor is the provision of means for driving the bits and operating them at various speeds in accordance with the requirements of particular drilling operations.

It is to be noted that the bits are inclined, as best shown in FIG. 1, so that the planes of the cutting surfaces of the cutters are inclined upwardly towards or in the direction of rotation of the unit In other words, the leading part of each cutter is higher than the trailing part, so that when the unit 23 is rotated the cutters have a milling action relative to the surface of the formation being cut and do not have to force themselves sideways into the formation.

Other types of bits may be used, such as diamond bits or the like, and under some operating conditions and with such bits it may not be necessary to incline the bits in the manner above pointed out. It is to be understood, too, that bits of different sizes and of diiierent tooth design may be used. It is important, however, that the bottom of the hole he acted upon by the bits and it is to be noted that the bits 46 as they operate are so arranged that as the unit 28 rotates on its axis said bits cut paths in the formation at the lower end of the bore hole 26, and these paths overlap so that with each revolution of the unit 28 the entire area of the bottom of the bore hole 26 is worked upon by said bits.

The usual means, not shown, for rotating the table 16 is provided on the platform to effect rotation of the drill string and hence the unit 28, the inner and outer strings of pipes rotating together. The lower end of the pipe 31, which carries the reamer 5S and bit 59, passes downwardly in the pilot hole 25 as the drilling unit 28 moves downwardly as the bottom of the bore hole 26 is cut away. The rearner 58 and bit 59 keep the pilot hole 25 open sufficiently so that there will be no sticking of the equipment during the drilling operation.

The conductor pipe is provided with a cover, indicated generally at 115, and said cover includes a top 116 having an axial opening therein in which is disposed a depending pipe 117' suitably secured at its upper end to said cover 116 by welding or other means. The top116 is reinforced by reinforcing members 118 which extend radially of the pipe 117 to the periphery of said cover 116 and at said periphery there is a depending flange 119 which has internal recesses 120 corresponding to the recesses or grooves 22 in the conductor pipe. The cover is sealed on the conductor pipe by means of hollow resilient tubes, which may be of rubber or other suitable material, and which are received in the grooves 22 and 120, which are in opposition to each other when the cover 115 is in proper position. Said tubes 1.21 are inflatable so as to provide a secure seal between the flange 119 and the conductor pipe 20. There is a valve 125 secured to the top 116 and communicating with the interior of the cover, said valve adapted to be connected to a suitable source of air pressure or other fluid under pressure for pressurizing the interior 126 of the conductor pipe and the bore 26.

Drilling fluid of suitable character, such as air or other gas, for example, is introduced into the annular passage 78 through a conduit 128 connected with an inlet pipe 129 of the swivel 80, as disclosed in the above referred to Grable Patent No. 2,701,122. This gaseous drilling fluid passes downwardly through the annular passage 78a between the branch pipes 82 and the branch pipes 65 and thence through the swivel connections 68 and into the passages 47, 48 and 5%, and nozzle discharge passage 54 of the respective bits. This fluid is directed onto the respective cutters 44 of said bits and flows upwardly into the pipes 46 and thence into the branch pipes 82 and into the interior passage of the pipe '76 and the corresponding pipes to which said pipe '76 is connected. The fluid passing through the bits picks up the cuttings and carries same upwardly into the swivel 8% from which said fluid and cuttings pass into the pipe 132 and hose 133 which carries same to a suitable disposal point.

In order to maintain fluid pressure in the interior 126 of the conductor pipe and in the bore 26, a rotary sealing device or head 135 is provided and is secured to the pipe 117, the drill string 75 extending through said head 135. Any suitable type of rotating sealing means may be used and such means or devices are well known in the art. These devices maintain the proper seal around the drill string and prevent escape of pressure while permitting the drill string to move upwardly and downwardly there through, as well as to rotate.

By pressurizing the bore 26 the cuttings are prevented from escaping outwardly from the bits and are kept within the effective flow paths of the drilling so that said cuttings will be carried upwardly through the pipes 46 and thence carried to the surface through the branch pipes and drill string.

Should it be desired to raise the unit 28 to replace bits or to otherwise service the unit, the pressure within the conductor pipe 26) and bore 26 may be released by means of the valve 125 and the fluid pressure within each pipe 129 is released. The cover and unit 28 may be raised to a point where said unit i readily accessible for servicing, or the like;

There is a cover for the unit 28 and said cover is three-armed so as to enclose the parts of the unit 28 between the plate 30 and the upper side of the branches 65. This cover is adapt-ed to be readily removedand also encloses ballast tanks 141 in which is suitable ballast, such as water or the like, which is used to provide ballasting means for the lower end of the drill string to minimize or eliminate any tendency of the equipment to deviate from the vertical during drilling operations.

Generally the drilling equipment is transported to the drill site on trucks, disassambled in component groups typical of oil field practices. The rig equipment can be transported in loads to conform with road and State highway limits.

Assembly and rig-up of a rig will conform essentially to common oil field practicesp After assembly of the drilling rig the pilot hole is drilled to a point below the depth to which the large bore hole is to be drilled.

After drilling the pilot hole this smaller equipment is disassembled. A larger diameter drill stem, which is concentric, as above described, is assembled and attached to a multiple drilling head through a solid cover plate and rotating packer assembly.

The drilling head or out 28 is slowly rotated on their respective axes. Air or other drilling fluid is supplied by pumps or compressors and circulated down the outer annulus 78 of the dual concentric drill string. Cuttings are picked "up by this fluid as the cutters of the bit cut same from the bottom of the bore hole and these cuttings are entrained in the drilling fluid which is returned to the surface upwardly through'the central annulus 79 of the drill string. At the surface the air stream discharge line 133 is connected to a separator which causes the cuttings to drop out of said stream. These cuttings may be transported easily and economically away from the drill site if desired.

It is believed that the invention and many of its attendant advantages will be understood from the foregoing description and it is believed that it will be apparent various changes may bemade in the process or method and the form, construction and arrangement of the parts of the apparatus of the invention without departing from the spirit and scope thereof or sacrificing all of its material advantages, the form hereinbefore described being merely by way of example.

We claim:

1. Apparatus for drilling large bore holes adapted to be lowered and raised by a drill string, comprising: an axial member having its axis substantially vertical; a supporting member axially secored to said axial member intermediate the ends thereof and rotatable therewith; a plurality of rotary drilling bits operably carried by said supporting member, said bits being inclined upwardly in the direction of rotation of said axial member and being variously spaced from said axial member so that when the axial member and supporting member are rotated said bits travel in annular concentric paths with edge portions of adjacent paths overlapping; and motor means for each bit for independently rotating same, said motor means being carried by said support member.

- 2. An apparatus for drilling large bore holes: bit supporting means adapted to be supported on a substantially vertical axis; a plurality of rotary drilling bits carried by said bit supporting means and having cutter elements, said bits being inclined upwardly relative to said vertical axis and to the direction of rotation, said bits being variously spaced radially from the axis of said supporting means so that when said means is rotated said bits travel in annular concentric paths with edge portions of adjacent paths at least meeting; power means for independently rotating each rotary bit; and support means for supporting said bit supporting means for vertical movement and for rotation on said substantially vertical axis.

. 3. An apparatus for drilling large bore holes; an axial member, bit supporting means carried by said axial member; 'a plurality of rotary drilling bits carried by said bit supporting means and having cutter elements, said bits being variously spaced from the axis of said means so that when said means is rotated said bits travel in annular concentric paths with edge portions of adjacent paths at least meeting; and ballast means on said bit supporting means for applying downward pressure on the supporting means.

4. An apparatus for drilling large bore holesz a rotatable bit supporting means adapted to be supported on a substantially vertical axis; a plurality of rotary drilling bits carried by said bit supporting means and having cutter elements, said bits being variously spaced from the axis of said means so that when said means is rotated said bits travel in annular concentric paths with edge portions of adjacent paths at least meeting, the bottom'plane of the cutter element being inclined upwardly in the direction of rotation of the supporting means to provide a milling action as the bits are moved in circular paths while cutting; means for rotating said bits; and means for supporting and rotating the entire mechanism on said vertical axis.

5. In apparatus for drilling large bore holes and the like: bit supporting means adapted to be supported on a substantially vertical axis; a rotary, drilling bit spaced from the vertical axis and carried by said bit supporting means and having cutter elements, the bottom plane of the cutter elements being inclined upwardly in the direction of rotationof thejsupporting means, means for rotating said drillingbit; and means rotatably supporting said bit supporting means for rotation on said vertical axis. 7

6. Apparatus for drilling large bore holes, comprising: an axial member; a supporting member axially secured to said axial member intermediate the ends thereof; a plurality of rotary drilling bits having cutter elements carried by said supporting member, said drilling bits having their axes of rotation somewhat inclined from the vertical so that the leading sides of said bits are higher than the trailing sides, said bits being variously spaced radially from said axial member so that when the axial member and supporting member are rotated said bits travel in annular concentric paths with edge portions of adjacent paths overthe first drill pipe string in concentrically spaced relationship thereto, the inner drill pipe string defining an inner passage and the annulus between the inner and outer drill pipe string defining an outer passage, fluid being adapted to flow downwardly in one-passage and upwardly in the other passage; respective conduit means for conducting downwardly flowing fluid in one of said passages to the drilling bits and discharging same against the cutters of the drilling bits; conduit means for conveying fluid from said drilling bits to the other'passage for upward flowing fluid; a conductor pipe at the upper end of the bore hole, said pipe being open at the upper end; a removable cover for the upper end of said conductor pipe, said cover having an axial opening therein for reception of the drill string, means releasably sealing said cover to said conductor pipe; and a rotary sealing device secured to said cover in axial alignment with said opening, said drill string being operably received in said rotary drilling head.

7. Apparatus for drilling large bore holes, comprising: an axial member; a supporting member axially secured to said axial member intermediate the ends thereof; a plurality of rotary drilling bits having cutter elements carried for rotation on substantially vertical axes by said supporting member, said drilling bits having their axes of rotation inclined from the vertical in a direction to position the leading sides of said bits higher than the trailing sides, said bits being variously spaced from said axial member so that when the axial member and supporting member are rotated said bits travel in annular concentric paths with edge portions of adjacentpaths overlapping; motor means for each bit for independently rotating same, said motor means being carried by said support member; means for controlling the speed of each motor means independently of the other motor means; a first drill pipe string connected to the axial member; a second pipe string of'smaller outside diameter than the inside diameter of the first drill pipe string disposed within the first drill pipe string in concentrically spaced relationship thereto, the inner drill pipe string defining an inner passage and the annulus between the inner and outer drill pipe string defining an outer passage, fluid being adapted to flow downwardly in one passage and upwardly in the other passage; respective conduit means for conducting said downwardly flowing fluid to the drilling bits and discharging same against the cutters of said drilling bits; and conduit means for conveying said fluid after same has been discharged against said drilling bits to the passage for upward flowing fluid. V a V 8. Apparatus for drilling large bore holes, comprising: an axial member having its axis substantially vertical; a supporting member axially secured to said axial member intermediate the ends thereof and rotatable thereby; a plurality of rotary drilling bits having cutter elements 7 operably carried by said supporting member, the axes of said bits being inclined upwardly in the direction of rotation of theaxial member so that the leading sides of said bits are higher than thetrailing sides thereof, said bits being variously spaced from said axial member so that when the axial member and'supporting member are rotated said bits travel in annular, concentric paths with edge portions of adjacent paths overlapping; motor means for each bit for independently rotating same, said motor means being carried by said supporting member; means for controlling the speed of each motor means independently of the other motor means; and a drill string conby said supporting member, said bits being inclined upwardly in the direction of rotation of said supporting member and being variously spaced from the axis of retation of said supporting member so that when the supporting member is rotated said bits travel in annular concentric paths; and means for rotating said bits on their respective axes.

10. Apparatus for drilling large bore holes adapted to be lowered and raised by a drill string, comprising: a supporting member adapted to be secured to said drill stem; a plurality of rotary drilling bits operably carried by said supporting member, said bits being inclined so that the trailing edges of said bits first engage the formation being cut and being variously spaced from the axis of rotation of said supporting member so that when the supporting member is rotated said bits travel in annular concentric paths; and means for rotating said bits on their respective axes.

References Cited by the Examiner UNITED STATES PATENTS 1,292,159 1/19 Trumpour. 2,074,951 3/37 Zublin 175-397 2,466,709 4/ 49 Karr.

10 2,701,122 2/55 Grable 17569 2,703,698 3/55 Westerman 255-306 2,758,825 8/56 Wohlmeyer. 2,887,301 5/59 Day 175334 2,890,022 6/59 Brown 175-334 2,930,586 3/60 Long 175-71 FOREIGN PATENTS 17,985 5/04 Austria. 197,767 5/58 Austria.

Aerated Mud Drilling, The Petroleum Engineer, page B-46, November 1955.

BENJAMIN HERSH, Primary Examiner.

Examiners. 

9. APPARATUS FOR DRILLING LARGE BORE HOLES ADAPTED TO BE LOWERED AND RAISED BY A DRILL STRING, COMPRISING: A SUPPORTING MEMBER ADAPTED TO BE SECURED TO SAID DRILL STEM; A PLURALITY OF ROTARY DRILLING BITS OPERABLY CARRIED BY SAID SUPPORTING MEMBER, SAID BITS BEING INCLINED UPWARDLY IN THE DIRECTION OF ROTATION OF SAID SUPPORTING MEMBER AND BEING VARIOUSLY SPACED FROM THE AXIS OF ROTATION OF SAID SUPPORTING MEMBER SO THAT WHEN THE SUPPORTING MEMBER IS ROTATED SAID BITS TRAVEL IN ANNULAR CON- 